<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS尺寸</title>
    <style>
        .LoginDiv{
            width:50%;
            height:50%;
            border:1px solid red;
            text-align:center;
        }
    </style>
</head>
<body>
<div class="LoginDiv">
    中北大学
</div>
<hr>
<input style="width:300px;height:20px" type="text" id="username" placeholder="用户名">
</body>
</html>